1. Field of the Invention
The present invention relates to discharging control devices for electric power conversion systems comprised of a DC power source, an electric power conversion circuit, a capacitor, and an electrical switching means (or a switch open/close means), and the discharging control device having a discharging control means for adjusting a charged voltage of the capacitor to a voltage of not more than a predetermined voltage by controlling the electric power conversion circuit when the electrical switching means is turned off (namely, opened).
2. Description of the Related Art
Conventional techniques, for example, Japanese patent laid open publication No. JP 2009-232620 discloses a conventional discharging control device. Such a conventional discharging control device is applied to an electric power conversion system. In general, such an electric power conversion system is comprised of a DC power source, an electric power conversion circuit, a capacitor, and an electrical switching means. The electric power conversion circuit converts a direct current (DC) voltage of the DC power source to a predetermined an alternating current (AC) voltage. The capacitor is placed between the electric power conversion circuit and the DC power source. The electrical switching means opens and closes electrical connections (wires or paths) between the electric power conversion circuit and the capacitor. The discharging control device is comprised of a discharging control means capable of adjusting a charged voltage of the capacitor to a voltage of not more than a predetermined voltage by controlling the electric power conversion circuit when the electrical switching means is turned off, (namely, opened).
The above conventional discharging control device makes a short circuit between both electrodes of the capacitor connected to an input terminal of the electric power conversion circuit as an inverter by simultaneously turning on a power switching element at a high voltage side and a power switching element at a low voltage side in the inverter in order to discharge the electric power charged in the capacitor. In particular, this conventional discharging control device as one conventional technique decreases a gate voltage of an Insulated Gate Bipolar Transistor (IGBT) as the power switching element during the discharging control in order to avoid an excess current from flowing between the electrodes of the capacitor when a short circuit is made between the electrodes of the capacitor. This discharging control operation is different from the usual control operation of the inverter,
By the way, the conventional discharging control device executes the above special discharging control operation by controlling the power switching elements and the capacitor. This special discharging control operation is different from the usual control operation. In other words, the usual control operation does not use the components of the electric power conversion system which are necessary to execute the special discharging control operation. Thus, the mechanism and components to be used for executing the usual control operation is different from the mechanism and components to be used for executing the special discharging control operation. Accordingly, to correctly drive the inverter comprised of the power switching elements and the capacitor during the usual control operation does not guarantee to correctly drive the inverter and the capacitor during the special discharging control operation of discharging the electric power charged in the capacitor. Therefore even if the usual control operation can be correctly executed and completed, there is a possibility that the special discharging control operation is not always executed correctly when receiving a request to execute the special discharging control.